1. Field of the Invention
The invention relates to spherical high-performance adsorbents with microstructure particularly adapted for the adsorption of gases and vapours in defined structural units, in particular in textile fabrics for the adsorption of chemical warfare agents and toxic gases and vapours, in support structures of adsorption refrigerating plants in the field of air conditioning engineering, in filter units for the adsorption of noxious gases and vapours in motor vehicles and in biofilters.
2. The Prior Art
It is known that spherical products which are produced in accordance with various methods from preformed starting materials or from carbonaceous materials and a binding agent can be used for the adsorption of particular gases and vapours.
The use of adsorbent ion exchanger resins for the removal of gaseous sulphur dioxide is described in German Laid Open document 2164261. In accordance with this method macroporous anion exchanger resins are used, however, the adsorption capacity is far below that of activated carbon. The adsorption capacity is instead comparable with active coke. Their suitability is limited to the adsorption of sulphur dioxide, without achieving the degree of separation of conventional activated carbon.
Partially pyrolysed particles of resin-type polymers for the removal of impurities from gases and liquids are known from East German Patent Specification 125340. The described particles are macroporous, with macropores in the range from 50 xc3x85 to 100,000 xc3x85 as the mean critical dimension. The atomic ratio of carbon to hydrogen is 1.5:1 to 20:1. By virtue of the missing activation stage, this product does not have an adequate adsorption performance and has an unfavourable pore distribution. As a result, this process only produces adsorbents of medium quality.
The spherical activated carbon which is described in DE 19538373 is manufactured on a base of a carbonaceous starting material and a binding agent. In the patent specification the suitability of the spherical activated carbon for the adsorption of hydrocarbons in motor vehicles exhaust is emphasized. The disadvantage of this product lies in the non-uniform spherical shape and the inadequate abrasion resistance. Moreover, no defined sphere diameters in the range of 0.3 to 0.7 mm are produced for technological reasons. The adsorption performance is inadequate for applications requiring high-performance adsorbents.
A formed activated carbon consisting of charcoal and betonite as a binding agent is described in DE 3712486 for the adsorption of petrol vapours in evaporation emission monitoring devices. The average grain diameter of the activated carbon is 3 mm. The disadvantage of this formed activated carbon lies in its low hardness and the associated high rate of dust formation, in the irregular shaping and the thus lower packing density and in the low bulk density in relation to the adsorption performance, which results in an unfavourable volumetric adsorption capacity.
Zeolites as adsorption agents are proposed in DE 4126960 and DE 4334808 specially for the application in adsorption refrigerating plants. However, they require a very high desorption temperature of 250xc2x0 C. in combination with the refrigerating agent water. For this reason they are not very effective in the utilisation of available quantities of heat. Another disadvantage in the application of refrigerating agents having operating temperatures below 0xc2x0 C., e.g. methanol, is that the adsorption performance is too low.
Micro-spheres, which consist of activated carbon particles under 0.1 mm which are bonded in water-insoluble artificial resins or of a distillation residue and a carbonaceous treatment byproduct, are known from DE 3510209 and WO 9807655. The structure of the micro-spheres consisting of several constituents results in a reduction in the available pore volume of the activated carbon constituent and thus in a lower adsorption performance. A further disadvantage is that the abrasion resistance is too low and the dust content too high.
The object of the invention is to make available spherical high-performance adsorbents for the adsorption of gases and vapours in defined structural units of textile fabrics, adsorption refrigerating plants, motor vehicle filters and biofilters. The adsorbents are to be distinguished by a very high adsorption capacity with respect to gases and organic vapours, a fine-grain fill associated with a high packing density for the achievement of a uniform layer structure to the single-layer covering, a high resistance to fracture, impact strength and abrasion resistance and extremely minimal dust constituent. The high-performance adsorbents have to be economical, without requiring large capital expenditures for equipment, employ simple technologies and also be reusable.
In this case it was discovered that spherical high-performance adsorbents, can be manufactured from polymer resins by water vapour activation with an activation time of at least 6 hours, resulting in a pronounced microstructure in the pore diameter range of 40 xc3x85 to 5 xc3x85 that they are able to absorb gases and organic vapours with a clearly higher capacity than the products of the prior art. More particularly, 5-10% of the overall micropore volume is between 20 and 40 xc3x85; 15-25% of the overall micropore volume is between 10-20 xc3x85; 10-20% of the overall micropore volume is between 8-10 xc3x85; 40-50% of the overall micropore volume is between 5-8 xc3x85; and 15-25% of the overall micropore volume is between 0-5 xc3x85. By this enlargement of the adsorption capacity the overall efficiency of the high-performance adsorbents is improved for use in defined structural units of diverse applications. Thus with the use of the adsorbents according to the invention in textile filter units or in fixed-bed filters, the adsorption capacity per surface or volume unit can be substantially increased without expensive construction measures. Pore densities of 0.6 cm3/g or higher may be obtained.
The spherical high-performance adsorbents specified by the invention have, apart from a distinctive microstructure, a uniform grain size distribution in the range of 0.315 to 0.7 mm, preferably 0.4 to 0.6 mm. More particularly, 84-95% of the particles have a grain size between 0.4-0.63 mm; 0.2-2.5% of the particles have a grain size between 0.63-0.7 mm; and 5-15% of the particles have a grain size between 0.315-0.4 mm. By this the formation of a fine-grain fill with high packing density is achieved, which even with a single-layer covering on a surface still has an effective degree of adsorption with respect to gases and vapours.
The resistance to fracture, impact strength and abrasion resistance of the high-performance adsorbents according to the invention is 100%, so that dust formation is practically non-existent. More particularly, less than 1% of particles are dust size, i.e. smaller than 0.04 mm. Consequently even in filter units subjected to strong mechanical stresses no impairment of the fill by dust or abrasion occurs.
The high-performance adsorbents according to the invention advantageously enable the application in textile fabrics for the adsorption of chemical warfare agents and poisonous gases and vapours and the inclusion of previously unused heat potentials in adsorption refrigerating plants by applying a fill to the heat exchanger faces inside the sorption unit, associated with a minimisation of the plant size. The high volumetric capacity and the very low dust content of the high-performance adsorbents according to the invention have a positive effect on the efficiency of filter units for motor vehicles and biofilter plants. Upto 2 grams absorbed substances per 100 cm3 adsorbent is possible. The ratio of weight capacity to volume capacity lies between 1.8 to 1 and 1.9 to 1, but is 2 to 1 at most.
This results both in lower requirements with respect to the quantity of adsorbent as well as in the advantage of a smaller size when compared with the known filter units. The dust-free handling of the high-performance adsorbents produces further advantages with respect to processing.
The spherical high-performance adsorbents specified by the invention are explained in further detail below by means of exemplified embodiments.